How To Repair Rotted Wood Window Sill

Q: Ane of our windowsills appears to be rotting. Can it be replaced without buying a new window?

—Bill Bailey, Baldwin, Mo.

David Raymond, Raymond Design Builders, replies: Sticking out into the weather year later on twelvemonth, wood windowsills take quite a beating. They can last for decades if y'all just keep them clean and protect them with a coat of paint. But when water gets trapped in or against them, as happens with improperly flashed windows, rot can accept hold.

A simple epoxy repair will do the pull a fast one on if the rot is confined to a minor area, but if more than x percent of the sill is rotten, the old sill should be cut off and replaced. For this projection, I used a solid piece of Kleer cellular PVC sill that matches the contour and thickness of the other sills on the house. It costs less than a piece of clear, milled red cedar and is paintable, only no thing how many times it gets wet, it can't rot.

Step-past-step tutorial renders below OTHER VIDEOS role player. Keep scrolling!

Step 1

Remove the Side Casings

The casing comes off to articulate the style for removing the former sill. If the casings are rotting, as here, supervene upon them, too. Slice through the caulk bead between the siding and the casing, and then carefully pry off each piece. Salvage the trim to employ as templates for the new ones. Make certain the flashing behind the casing is intact and properly installed behind the siding.

Step two

Saw Off the Former Sill

Make a plumb cut flush with the capsule forth the length of the rotten sill. A circular saw with a beveled bract tin handle most of the cut, but for the sill ends where a circ saw can't reach, switch to a multitool, like this Fein Multimaster equipped with an aquiver saw bract. Smooth the cut with a few strokes of a hand plane.

Stride 3

Apply the Adhesive

Repair whatsoever rotten spots on the old sill with epoxy. Trim the back border of the new sill every bit needed and then that its lower edge fits tightly against the siding and its back edge fits against the old woods. Drill pilot holes every 16 inches or so through the new sill'southward front and back edges. Run a dewdrop of waterproof, marine-grade adhesive along the old sill.

Step 4

Adhere the New Sill

Press the new sill into the adhesive, and immediately clamp information technology in identify by driving iii½-inch deck screws through the plastic and into the woods. Finish when the heads are about ¼ inch below the sill surface. Immediately wipe up any adhesive that squeezes out. Fill up whatsoever gaps between the old and new sill with adhesive.

Step five

Hide the Screwheads

Comprehend each screwhead with a dollop of a white, 2-part acrylic adhesive, such every bit Bail&Fill FastCure. (This besides works as an adhesive in Footstep iii.) Overfill the recess slightly. When the adhesive hardens completely, in about 30 minutes, sand it flush.

Stride 6

Install the Side Casing

Squeeze a dewdrop of caulk beside the ends of the siding, and blast the new casing in place. Here, I used cellular PVC trim boards and 8d stainless-steel band-shank nails. Gear up the nailheads slightly below the surface, and cover each one with a dab of the two-role agglutinative. After the dabs harden, sand them flush.